Until recently, chlorofluoroalkane-based blowing agents (CFCs) such as CFC-11 (CCL.sub.3 F) have been the most desirable blowing agents for the preparation of isocyanate-based foams, such as rigid and flexible urethane and isocyanurate foams because of their many advantages including low thermal conductivity, nonflammability of the blowing agent and good dimensional stability of the resulting foam. However, it is becoming increasingly obvious that there may be an association of certain CFCs with the declining ozone concentrations from the earths atmosphere. As a consequence, the use of certain CFCs is being restricted and thus alternative blowing agents are necessary for the preparation of foam.
As a preliminary solution to this problem, hydrogen-containing chlorofluoroalkanes (HCFCs') such as HCFC-123 (CHCl.sub.2 CF.sub.3) and HCFC-141b (CH.sub.2 ClCHCLF), which have relatively short life times in the atmosphere and essentially decompose before they reach earths' stratosphere containing the ozone, have been proposed. These alternative blowing agents however, present the disadvantages of frequently poorer processing, relatively higher thermal conductivity and often inferior dimensionally stabilities of the resulting foam especially when used in combination with water blowing.
The thermal insulation performance of a foam is dependent principally on the average thermal conductivity of the gas mixture contained within the cells and especially the cell size. Carbon dioxide has a gas thermal conductivity which is significantly greater than that of most "soft" halocarbons and therefore its presence in the gas mixture contained within the cell can be disadvantageous for optimum thermal insulation performance of the foam. With respect to cell size, enhanced thermal insulation performance is generally obtained with a smaller average cell size. Therefore to compensate for any increased average thermal conductivity of the gas that may be contained within the cells of the foam it is desirable to develop new foaming processes which provide for a foam having a fine cell size.
In a recent European Patent publication, EP 351614, fine celled polyurethane foam is prepared in the presence of a blowing agent which is a fluorinated hydrocarbon and/or hexafluorosulphur and being poorly soluble or insoluble in the foam precursor materials. An emulsifying agent, particularly an oligomeric acrylate polyoxyalkylene substance containing fluoroalkane residues is taught as being necessary to provide for resulting foams which do not collapse.
To this purpose of providing a process allowing for the preparation of fine-celled foam we have investigated use of foaming or blowing agent mixtures containing polyfluorocarbon compounds including above mentioned fluorinated hydrocarbons with other physical blowing agents in the preparation of cellular products.